Apertured vane magnetron



March 25, 1958 JENNY I 2,828,441

APERTURED VANE MAGNETRON Filed Dec. 24, 1954 2 Sheets-Sheet 1 4 INVENTOR. HAM s KJiA/A Y 2 She ets-Sheet, 2

R w w S RN 7 \m March 25, 1958 H. K. JENNY APERTURED VANE MAGNETRON Filed Dec. 24, 1954 United States 2,828,441 APERTURED VANE MAoNErnoN Hans K. Jenny, Whippany, N. 3., assignor, by mesne assignments, to the United States of America as repra Sealed bythe' S'ecita'ryof the Navy Application December 24, 1954, Seriai No. 477,5ii2 6 Claims. ci;-3'1s--s.is

cavity resonators, by means of which a signal may be employed to modulate the magnetron output.

It is' afurther object to enable a modulated electron Beam to be directed tangentially into the anode structure of a magnetron, thereby to provide a modulated radio frequency output signal.

It is a further object to provide an improved magnetron by which an input signal may be amplified.

It is'a still further object to provide an improved magnetron for use as a reactance tube.

In one aspect, the invention comprises an oscillator magnetron having a plurality of partitions or vanes extending radially from the central cathode region to define a plurality of cavity resonators circumferentially separated by drift spaces. The inner portions of the vanes or partitions are apertured to permit electrons to pass thru the inner regions of the cavity resonators where relatively high electric field strengths exist. By this construction, a high degree of coupling is attained between the electron stream and the cavity resonators. Accelerator electrodes are positioned in the drift spaces to control the paths of the electrons, and a modulating signal may be applied to the accelerator electrodes to provide a modulated radio frequency output signal. According to another form of the invention, an additional partition is employed to deootiple the cavity resonators from each other, an input signal is coupled to one of the cavity resonators, and an amplified output signal is coupled from another of the cavity resonators. According to a further form of the invention, a modulated electron beam is directed tangenany into the anode structure, and a correspondingly modulated radio frequency output signal is taken from oneof the cavity resonators.

1 These and other objects andaspects of the invention will be apparent to those skilled in the art from the following more detailed description taken in conjunction with the appended drawings wherein:

Figure l is a perspective cut-away view of a magnetron constructed according to the teachings of this invention for use asan oscillator;

Figure 2 is a t ansverse sectional view taken thru the anode structure of the magnetron shown in Figure 1;

Figure 3 is a longitudinal sectional view taken on the line 33 of Figure 2;

V '4 is a perspective view, having portions broken snowmen interior details, of an anode structure of atent 2 the hole-and-slot type, rather than the vane type shown in the other figures; Figure 5 is a perspective view, with portions broken away to show interior details, of an anode structure according to this invention for use in an amplifying magnetron;

Figure 6 is a transverse sectional-view taken thru the anode structure of Figure 5;

Figure 7 is a longitudinal sectional view lines 7-7 of Figures 5 and 6', V

Figure 8 is a transverse sectional v'iew of the anode structure portion of a magnetron constructed according to this invention which is useful for generating a signal modulated radio frequency wave; and

Figure 9 is a transverse sectional view taken on the line 9-9 of Figure 8.

Reference will now be made to Figures 1' thru 3 showing an oscillator magnetron constructed according to this invention. The magnetron includes an evacuated envelope 10 including magnetic polepieces 11 and 12. In use, the magnetron is'positioned' with the pole pieces 11 and 12 in alignment with the north and south poles of a permanent magnet 13. A cylindrical cathode 14 is positioned axially in the envelope 10' of the magnetron and electrical connections are made thereto by means of leads 15 and 15.

An anode structure generally designated 16 includes a plurality of radially extending metallic vanes or partitions 17 extending from the region of the cathode 14. The partitions I7 define the side of a plurality of cavity resonators 18 separated by drift spaces 19. The outer ends of adjacent partitions 17 are connected by a conductive wall member 20serving to close the'outer ends of the respective cavity resonators 18. Conductive end plates 2-1 and 22 disposed at right angles with the axis of the magnetron include radial portions connected between adjacent partitions-.17 to close the ends of the drift spaces 19. These end plates 21 and 22 do not cover the cavity resonators 18'. The inn'erpo'rtions of the vanes 17 are provided with apertures to provide a grid-like structure as represented at 25in Figures 2 and 3. Any suitable grid-like structure may be employed. The electron permeable portions may consist of parallel spaced wires, wire mesh, slotted metallic sheets, or any other construction which provides apertures thru which electrons may readily pass.

Accelerator electrodes 26 are positioned in the drift spaces 19 and are connected to a common metallic contact ring 27 mounted in insulated relation on the member 20' by suitable means (not shown). A lead 28 is taken thru the evacuated envelope 10 from the contact ring 27 to provide an external connection for the application ofactaken on the celerat-ing potentials to the accelerating electrodes 26. I

The coupling between cavity resonators 18 is increased by means of straps 29' thru 32; Straps 29 and 30 are connected to alternate radial portions of endplate 21, and straps 31 and 32 are similarly connected to alternate radial portions of end plate 22 The cathode 1'4 is preferably constructed to include longitudinally extending stripsi3'5 ofthermo-emis'sive' material, the strips being positioned opposite-the drift spaces 19 .containin'g the accelerator electrodes 26. Radio frequency energy is' taken out from the magnetron by means of a coupling loopi36; located in one of the cavity resonators 18 and connected to an outputcoaxial line 37.

In the operation of the oscillator magnetron shown in Figures 1 thru 3, some ofthe electrons emitted-from the thermoeniiss'ive st-rips are caused to take a generally spiral course-outwardly under the influence of the axial magnetic field and the accelerating potentials -app'lie'd t0 the accelerator electrodes 26 and to'the anode structure 16. Depending on the geometry of the apertured vanes,

most of the electrons take an outwardly spiraling course passing thru the openings in the vanes. Ultimately, the electrons strike some part of the anode structure 16, or return to the cathode 14. a

By the construction according to this invention wherein thevanes or partitions 17 are apertured at their inner ends, a greater proportion of the electrons rom the cathode 14 pass thru the cavity resonators 18 and interact with the electric fields therein. According to prior art constructions, the electrons merely pass by the opening between the vanes defining the cavity resonators. It will be noted that the vanes 17 are not apertured throughout their entire length but only at their inner portions Where the electric field strengths are the greatest. By the construction including drift spaces 19 between adjacent cavity resonators 18, and by the use of accelerator electrodes 26 in the drift spaces, it is possible to control the trajectories of the electrons for optimum performance. A synchronizing signal may be applied to the accelerator electrodes by means of the lead 28 to control the frequency of oscillation of the magnetron.

Figure 4 shows an anode structure equivalent in all respects to that shown in Figures 1 thru 3. The construction shown in Figure 4 follows the hole-and-slot arrangement. The partitions 17' which are provided with openings at 25' extend substantially radially from the center region of the magnetron. The end members 2%" close the peripheral ends of the cavity resonators formed by the partitions 17'. End plates 21 and 22' include radial portions which close the ends of the drift space cavities in a manner similar to that shown in Figures 1 thru 3 but do not cover the cavity resonators. The form of the invention shown in Figures 1 thru 3 is simpler to construct and is therefore generally more desirable than the form shown in Figure 4. a The invention as exemplified in Figures 1 thru 4 is not limited to use as a simple oscillator, but may be employed as an amplitude modulated oscillator or a frequency modulated oscillator by applying a modulating signal to the terminal 28 connected to the accelerator electrodes 26, and/or to the anode block 16. The modulating signal causes a modulation of the amplitude or the frequency of the radio frequency oscillation having a frequency determined by the geometrical dimensions of the cavity resonators. By the construction shown and described, amplitude modulation may be obtained with less undesired incidental frequency modulation than is possible with prior art devices. Similarly, frequency modulation may be obtained with less accompanying amplitude modulation.

By operating the magnetron at currents lower than required for operation as an oscillator, the magnetron operates as a reactance tube wherein the frequency of a resonant circuit is made to vary in accordance with the magnetron current. According to this invention the magnetron employed as a reactance tube has been found to provide about ten times as great a frequency or reactance change as that obtainable with standard vane type magnetrons.

Figures 5 thru 7 show a magnetron anode block constructed according to this invention for operation as a radio frequency amplifier. In Figures 5 thru 7, elements are given the same numerals as appear on corresponding elements in Figures 1 thru 3. In addition to the output loop 36 and output coaxial line 37, there is provided an input coaxial line 40 connected to an input coupling loop 41 disposed in one of the cavity resonators 18. The cathode 14 is provided with a single strip 35, of thermoemissive material, the strip being disposed opposite the drift space 19 which is between the input and output cavity resonators 18. Some of the electrons from the thermocmissive strip 35' take an outwardly spiraling course, as represented by the arrow in Figure .6, thru the input cavity resonator, and around to the right suc- 4 cessively thru the other cavity resonators and drift spaces to the output cavity resonator. The vane or partition 17" located between the output cavity resonator and the cathode strip 35' is not apertured and therefore prevents electrons from going more than 360 degrees around the anode structure from thermo-emissive strip 35. By making the vane 17" solid (electron impermeable) rather than electron permeable, the magnetron is prevented from oscillating. The input signal applied thru input line 40 appears as amplified signal at the output line 37.

in addition to making the vane 17" between the output and input cavity resonators solid, further measures are taken to decouple the cavity resonators to prevent undesired oscillations. These further measures include conductive cup-shaped end-closures 44 and 45 on both ends of the anode structure 16 having annular lips connected to the peripheral edges of the plates 21 and 22, and radially extending conductive partitions 47 connected between the end-closure 44 and the radial portions of end plate 21 closing the drift spaces 19 and radially extending conductive partitions 48 connected between the cupshaped end-closure 45 and the radial portions of conductive end plate 22. The cup-shaped end-closures 44 and- 45 together with the radially extending conductivepartitions 47 and 48 prevent coupling between adjacent cavity resonators by means of magnetic lines of force extendaround the exterior of the drift spaces defined by vanes 17 and end plates 21 and 22. The construction is such as not to short-circuit the electric field extending between the vanes 17 defining the cavity resonators.

It is apparent that according to the construction described in connection with Figures 5 thru 7 that there is provided a magnetron useful for amplifying radio frequency signals and constructed with apertured vanes and accelerator electrodes in drift spaces to provide the advantages described in connection with the oscillator magnetron shown in Figures 1 thru 4. It will, of course, be understood that the anode structure shown in Figures 5 thru 7 is employed within an evacuated envelope n1ounted within a magnet after the manner illustrated in Fig ure 1. V

Figures 8 and 9 show the anode structure portion of a magnetron for use as a modulated oscillator wherein the modulating input to the anode structure is in the form of a velocity modulated electron beam directed tangentially into the anode structure. The corresponding elements in the arrangement of Figures 8 and 9 are given the same reference numerals as appear-in the oscillator arrangement of Figures 1 thru 3. Cathode 14 is a dummy cathode in that a relatively negative potential is applied thereto, but no thermo-emissivecoating is provided since the necessary electrons originate in a source external of the anode structure. A velocity modulated electron beam is directed tangentially into the anode structure from a conventional electron gun and input cavity resonator arrangement generally designated 50. In order to direct the electron beam tangentially into the anode structure 16, it is necessary to provide a vacant cavity 51 which is somewhat in the nature of a drift space cavity without an accelerator electrode. The beam then passes thru the successive cavity resonators 18 and drift spaces 19 under the influence of the axial polarizing magnetic field and the potentials applied to the dummy cathode 14, the accelerator electrodes 26, and the anode structure 16. The electrons in the velocity modulated beam become bunched in the magnetron due to the pattern of velocity differences of the electrons leaving the gum and input cavity resonator arrangement 50. An interchange of energy results between the electron beam and the cavity resonators 18 whereby the output from coaxial line 37 isa radio frequency signal modulated in accordance with the input signal applied to the input coaxial line 52. f

It will be noted that all forms of the invention include the advantageous construction whereby cavity resonators are separated by drift spaces, the vanes or partitions defining the cavity resonators being apertured at their inner portions to enable electrons to pass therethrough at locations where the electric field strentghs are the greatest. Accelerating electrodes are provided in the drift space cavities to provide means for controlling the paths taken by the electrons. The radially outer portions of the vanes or partitions are solid rather than apertured to accommodate the high surface currents which flow in the corresponding portions of the cavity resonators. It is apparent that according to this invention there is provided a magnetron construction whereby a greatly increased inter-action or transfer of energy is accomplished between the electron beam and the cavity resonators.

What is claimed is:

1. A magnetron including an anode structure comprising a plurality of conductive partitions extending substantially radially from the region of an axis and conductive wall means connecting the outer ends of adjacent partitions to define a plurality of cavity resonators circumferentially separated by drift spaces, the inner portions of said partitions being provided with openings to enable electrons to pass therethrough, and conductive end plates at right angles with said axis including portions connected between the partitions that define said drift spaces to close the ends of said spaces.

2. A magnetron as defined in claim 1, and in addition, accelerator electrodes positioned within said drift spaces.

3. A magnetron as defined in claim 2, and in addition, annular straps connecting alternate ones of said portions of said end plates for operation of said magnetron as an oscillator.

4. A magnetron as defined in claim 2, and in addition, two conductive cup-shaped end-closures on both ends of said anode structure and having annular lips connected to the peripheral edges of said end plates, and radially extending conductive partitions connected from said endclosures to said end plates, whereby said cavity resonators are decoupled from each other for operation of the mag netron as an amplifier.

5. A magnetron as defined in claim 1, and in addition, annular straps connecting alternate ones of said portions of said end plates, means to inject an electron 'beam tangentially into one of said cavity resonators, and an output coupling from another of said cavity resonators.

6. A magnetron as defined in claim 5, and in addition, means to velocity modulate said injected electron beam.

References Cited in the file of this patent UNITED STATES PATENTS 2,408,903 Biggs et al. Oct. 8, 1946 2,419,172 Smith Apr. 15, 1947 2,637,004 Malter Apr. 28, 1953 2,642,551 Litton June 16, 1953 

